The present invention relates to laser diode assemblies.
Laser diodes offer both high output power and a small footprint, making them good candidates for many applications including materials processing, medical devices, telecommunications, printing, and other uses. The output of the laser diode can be coupled to an optical fiber serving as a waveguide or providing a laser cavity for a fiber laser. The optical fiber's input surface is typically circular, while the laser diode's output beam is roughly an elongated rectangle. Therefore, direct coupling of the output beam into the fiber is inefficient, underutilizing the fiber's input area and hence the fiber's capacity for input brightness and power.
To increase the brightness and power coupled into the fiber, output beams of multiple laser diodes can be stacked above each other (i.e. with the long axes stacked above each other) to more closely approximate a circle. The long axis of a laser diode's emitter is called a “slow axis” due to low divergence of the beam along this axis. This axis is parallel to the diode's pn junction. The emitter' short axis, which is called a “fast axis” due to higher divergence of the beam along this axis, is perpendicular to the pn junction. For manufacturing convenience, the laser diodes can be manufactured in a single semiconductor structure in a laser diode bar configuration, with their slow axes positioned on a single line, and the beams can be placed into a stack using turning mirrors. See e.g. U.S. Pat. No. 6,044,096 issued Mar. 28, 2000 to Wolak et al. See also U.S. Pat. No. 6,898,222 issued May 24, 2005 to Hennig et al., describing another configuration in which the laser diodes' slow axes are not on a single line to form a stepped configuration.
Even minute misalignments between the laser diodes and the optical components (such as turning mirrors and the collimating and focusing optics) may reduce the coupling efficiency between the laser diodes and the optical fiber.